This invention relates to the recovery of bromine from bromide ion solutions, and more particularly, to an electrolytic process for the recovery of bromine from alkali metal bromide and hydrobromic acid solutions and to the recovery of bromine from such solutions which are contaminated with organic material. The invention also relates to the electrolysis of mixed halide solutions and to the production of hypobromous acid solutions from mixed halide solutions.
Bromine and bromine releasing compositions have been demonstrated to be useful for numerous industrial and consumer applications. These applications include disinfection and other biological control in connection with recirculating cooling water, waste water, pond and lagoon water, bleaching, irrigation, metal extraction, and swimming pools, among others. Other applications include use of bromine in a manner unrelated to its capacity for disinfection/biocontrol, such as in the manufacture of brominated organic compounds.
In the manufacture of brominated organic compounds, molecular bromine reacts with an organic substrate to produce HBr as a by-product: EQU RH+Br.sub.2 .fwdarw.RBr+HBr
where R is an organic functional group. The HBr by-product may be absorbed in an aqueous medium to produce hydrobromic acid solution. Alternatively, the HBr by-product may be absorbed in sodium hydroxide solution to produce an alkaline by-product solution of sodium bromide.
Organic bromine compounds are commonly used as intermediates in the manufacture of other organic products. For example, an organic bromide can be reacted in an aqueous medium with a nucleophile which displaces the bromide to produce an organic compound substituted with the nucleophile, plus Br.sup.- as a by-product. For example: EQU RBr+M.sup.+ +Nu.sup.- .fwdarw.RNu+M.sup.+ +Br.sup.-
where Nu.sup.- is a nucleophilic anion and M.sup.+ is either an alkali metal ion or hydrogen ion. By-product alkali metal bromide solutions of the nucleophilic substitution are commonly contaminated with significant amounts of organic materials, typically in proportions of over 1000 ppm. Hydrobromic acid and sodium bromide solutions obtained in recovering HBr from organic bromination operations may be similarly contaminated. Unless such by-product streams can be further processed to separate the organic materials from the bromide ion, the latter is entirely wasted, resulting in an unfavorably high consumption of bromine and bromine sources in the manufacture of the RNu product.
The bromide content of many organic bromination or nucleophilic substitution waste streams represents a substantial economic value if recovered as molecular bromine. In any case, increasingly restrictive regulation of chemical waste effluents makes recovery of many materials a necessity, regardless of economic return.
Conventionally, bromine is produced in the first instance by chlorine oxidation, i.e., by contacting a bromide ion solution with chlorine gas. This reaction is normally carried out in a packed tower in which an alkali metal bromide brine is contacted with chlorine and steam. The chlorine reacts with the bromide ion to produce molecular bromine and by-product chloride ion: EQU 2Br.sup.- +Cl.sub.2 .fwdarw.Br.sub.2 +2Cl.sup.-
A mixture of Br.sub.2, Cl.sub.2, and steam exits the top of the tower and is cooled to condense Br.sub.2. Chlorine oxidation technology can also be brought to bear on the recovery of molecular bromine from bromide ion-containing waste streams. However, this process consumes chlorine and produces a waste solution containing substantial amounts of by-product chloride ion. Moreover, certain by-product streams contain high molecular weight organic residues that may tend to plug the chlorine oxidation tower.